Possible security problem - not sure

[Rosalie]

Dear Zen Cart team
Recently, a new customer (i.e. someone who had set up a new account for himself in the normal way) made a purchase in the normal way.
However, according to Zen records, he seemed also to have made a second purchase (different items) EXCEPT for the invoice and delivery address. These were obviously entered by another new customer but somehow bringing his email address forward into their account. (Ncidentally, there was no problem with payments - i.e. the first customer was charged for his order and the second customer was charged for her order i.e. correctly.)
We have recently updated the site with the latest Zen version which has been working fantastically. I just wondered if this small hitch could be resolved.
Many thanks for any help.

[Merlinpa1969]

Its most likely that both of these shoppers came in on a link posted somewhere that has the zen-id attached to it,

that is the session ID and if posted with a link can easily cause this kind of issue